Re: Var. skin imped. match



Paul Lewis wrote:
I refer to figure 4 in the interesting paper below. It is a chart
showing that skin impedance varies from 100 Ohms to 100K Ohms across
the 1MHz to 100Hz range.

I need to build a variable impedance matching circuit for
micro-current skin electrodes that covers this full range.
I am a graduate student in biophysics, but not an electronics
engineer.

https://upcommons.upc.edu/e-prints/bitstream/2117/1401/4/ROSELL-COLOMINAS.pdf

Can anyone suggest an appropriate circuit?

Paul Lewis
SCU



http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=497047

"Electrodes with impedance matching at the sensing site are referred to as active electrodes and have been designed since 1960's [15-17]. The electronic part of these transducers mostly consists of a buffer amplifier, but some have been designed to need only two lead connection wire [18,19]. However, as the signal is not amplified, buffers introduce significant noise and a low noise amplifier is still needed at the front-end. In order to avoid this drawback we used a two-op-amp biopotential amplifier [20] shown in Fig. 3, where op-amps A0 and A1 were integrated at the electrodes (Fig. 4), instead of using extra buffers. This resulted in lower noise and less parts, at the expense of increased number of electrode leads. The amplifier is based on the two-op-amp instrumentation amplifier shown in Fig. 5. The output voltage of the basic two-op-amp amplifier is..."

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